1. Field of the Invention
The invention relates to a zoom lens and an image pickup apparatus equipped with the zoom lens, and more particularly, to a zoom lens suitable for an image pickup apparatus using a solid-state image sensor such as a video camera, an electronic still camera, a broadcasting camera, and a monitoring camera or an image pickup apparatus such as a silver-halide film camera.
2. Description of the Related Art
In recent years, in a photographic optical system used in an image pickup apparatus using a solid-state image sensor, there is a demand for a zoom lens having a miniaturized size with a high zoom ratio and a high resolution. In addition, there is a demand for an image-stabilizing mechanism for compensating for an image shake generated when accidental vibration such as a camera shake is transferred to the zoom lens. Particularly, when correction is made by moving a correction lens unit for image shake correction in a direction perpendicular to an optical axis, the correction lens unit is required to have a small size and a light weight to miniaturize the image-stabilizing mechanism and save power. Furthermore, there is a demand for a photographic optical system that experiences little variation of aberration during the image shake correction and maintains excellent optical performance during the image stabilization.
There is known a positive lead type zoom lens in which a lens unit of a positive refractive power is arranged closest to an object side with an image-stabilizing function.
U.S. Pat. No. 7,894,135 discusses a five-unit zoom lens including first to fifth lens units of positive, negative, positive, negative, and positive refractive powers, respectively, in order from an object side to an image side, in which the fourth lens unit includes a single component, and image shake correction is performed.
U.S. Pat. No. 7,525,729 discusses a five-unit zoom lens including first to fifth lens units of positive, negative, positive, positive, and positive refractive powers, respectively, in order from an object side to an image side, in which the fifth lens unit includes three lens sub-units, and image shake correction is performed using a part of the lens sub-units.
U.S. Pat. No. 7,652,688 discusses a five-unit zoom lens including first to fifth lens units of positive, negative, positive, positive, and negative refractive power, respectively, in order from an object side to an image side, in which the fifth lens unit includes two lens sub-units, and image shake correction is performed using a part of the lens sub-units.
In addition, there is known a rear focus type zoom lens in which focusing is performed by moving a lens unit other than an object-side first lens unit to miniaturize the entire zoom lens.
U.S. Pat. No. 6,094,312 discusses a zoom lens including first to fifth lens units of positive, negative, positive, negative, and positive refractive powers in order from an object side to an image side, in which zooming is performed by moving the second lens unit, and focusing is performed while an image plane variation caused by the zooming is corrected by moving the fourth lens unit.
The image shake can be corrected relatively easily using a zoom lens in which a part of the lens units thereof is used as an image-stabilizing lens unit, and they are decentered in parallel to the direction perpendicular to the optical axis to perform the image shake correction. However, if a high zoom ratio is to be obtained while a configuration of the zoom lens and a configuration of the image-stabilizing lens unit moved for image stabilization are not appropriate, a large amount of decentering aberration is generated during image stabilization, so that optical performance is significantly degraded. For this reason, in a zoom lens having an image-stabilizing function with a high zoom ratio, it is important to appropriately set a configuration of the entire lens or a configuration of the lens unit included in the correction lens unit for image stabilization.
For example, it is important to appropriately set a refractive power and an image-forming magnification of the image-stabilizing lens unit, an image-forming magnification of a lens unit located on the image side of the image-stabilizing lens unit, and the like. If such configurations are not appropriately set, it is difficult to miniaturize the entire zoom lens and maintain excellent optical performance during image stabilization with a high zoom ratio.